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Imaging Sensor - Controls and Definitions

Updated: Dec 22, 2020

The scope of this article is to introduce you to the controls that the camera provides that give you control on the imaging sensor directly.


The 4 basic controls that you can adjust on the sensor itself are:

→ Resolution

→ Gain

→ Exposure Time

→ Black Level Compensation (Brightness)


Resolution


Every sensor supports 2 or more resolution options inherently. We shall be able to control the resolution settings. For example, if we are looking at a 640x480 resolution sensor, we also get options to select 320x240 resolution.


Before we select the camera, we need to analyze what is the resolution required for the use case. The various aspects we have to consider with respect to resolution are:

1. Higher number of pixels enable us to achieve higher details

2. More pixel à small pixel size à lower SNR

3. Smaller pixels increases the difficulty for lenses to resolve

4. Always plan for lowest resolution that can satisfy the use case.

5. Higher resolution à higher price


Gain


The gain control gives us the access to amplify the analog signal from pixel before conversion. The benefits of the gain control is that we can have higher grey scale level. The disadvantages of gain control is that it adds noise.


Before we plan to use gain control, we need to understand the below aspects

→ Increasing the gain value will impact in an increase in the signal level as well as

the noise level.

→ Gain control does not increase the image quality.

→ Gain control should be used as the last resort to increase brightness

→ Gain control can have limitations at higher bit depths.


Exposure Time


Exposure time is the duration of time that the sensor open for collecting light. This term is often analogous with integration time or shutter speed.


Exposure time is a critical control that lets you control the amount of light that falls on the sensor. This duration helps the sensor capture the scene. However, before we use the exposure time control, we need to have an understanding on the below aspects

→ More the exposure time, more the pixel well fills up. This results in a higher SNR.

→ Increase in the exposure time would essentially reduce the frame per second.

→ More the exposure time, there are more chance of motion blur.


Black Level Control


Black Level control enables us to add an offset to the pixel values. When we increase the black Level settings, we can expect a positive offset in the digital values output for the pixel and when we decrease the black level settings we can expect a negative offset in the digital values of the pixel. Unlike gain, Black Level enables you to work on the digital signal rather than the analog signal.


These are the controls that are directly interacting with the sensor. These controls are true for both Monochrome sensor as well as RAW Bayer sensor based cameras. We shall be covering more on the 2 types of cameras in further articles.

Should you have any queries, please feel free to get in touch with us.


Sarvesh Rajagopal

sarvesh@regami.solutions


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